1. Field of the Invention
The present invention relates to an organic electroluminescent element (hereinafter referred to as an organic EL element) comprising one or more organic thin films (hereinafter referred to as an organic functional layer) including a light-emitting layer consisting of organic compound material which exhibits electroluminescence when electrical current is injected thereto. More particularly, the present invention relates to an electroluminescent display panel (hereinafter referred to as organic EL display panel) with one or more organic EL elements formed on a substrate.
2. Description of the Related Art
The organic EL element fundamentally comprises an anode and a cathode with one or more organic functional layers layered between them. In the light-emitting layer of the organic EL element, an electron and a hole injected from both electrodes recombine with each other to form an exciton. When the exciton changes its state from an excited state to a basic state, it emits light. For example, an organic EL element has an anodic transparent electrode, an organic functional layer, and a cathodic metal electrode, which are sequentially deposited on a transparent substrate so as to emit light through the transparent substrate side. The organic functional layer can be formed in a laminate form of a single light-emitting layer, or of a three-layer structure which includes an organic hole transport layer, a light-emitting layer and an organic electron transport layer, or of a two-layer structure which includes an organic hole transport layer and a light-emitting layer. At least one of an electron injection layer, a hole injection layer and a carrier block layer may be inserted among the abovementioned layered layers and both electrodes.
As organic EL display panels, for example, the matrix display type and the panel having a predetermined luminescence pattern are well known.
When this organic EL element is exposed to the atmosphere, it is easily degraded by water, gasses such as oxygen, and some type of molecule in the operating environment. In particular, the properties of the interface between the electrode of the organic EL element and the organic functional layer deteriorate markedly, and the luminescent properties, such as brightness and color, also deteriorate. To prevent such adverse influences, in the case of the organic EL display panel, the organic EL element is sealed with a single inorganic protective film, such as silicon oxide, to restrain its deterioration. However, such a protective film does not have sufficient barrier properties. That is, it is impossible to avoid the generation of pinholes in the inorganic barrier film. When pinholes are formed in the protective film, then water, oxygen or the like can penetrate the film, and a non-luminescent spot of the organic EL element, a so-called dark spot, spreads out.